Weight indicator for rotary drilling



0d. 1942- E H. LAMBERGER EIAL 2,298,216

WEIGHT INDICATOR FOR ROTARY DRILLING Filed Sept. 26, 1939 3 Sheets-Sheet1 fl I wrmsssss;

INVENTORS ATTORNEY 1942- E. H. LAMBERGER ETAL 2,298,216

WEIGHT INDICATOR FOR ROTARY DRILLING Filed Sept. 26, 1939 3 Sheets-Sheet2 Fly. 2.

Edward II. Zambe Bernard F L WITNESSES:

er 8 er.

glmk Juli ATTORNEY 1942- E. H. LAMBERGER ETAL ,298,216

WEIGHT INDICATOR FOR ROTARY DRILLING 12 13 32 31a mDj Total Load on LoadBottom 4.0. Supply WITNESSES: INVENTORS g l I 1 Edward HLambez-ga' 8 I WBernarz l F'Lanyer.

ATTORNEY Patented Oct. 6, 1942 WEIGHT INDICATOR FOR ROTARY DRILLINGEdward H. Lamberger, Wilkinsburg, and Bernard F. Langer, Pittsburgh,Pa., assignors to Westinghouse Electric 4; Manufacturing Company, EastPittsburgh, I'a., a corporation of Pennsyl- Vania Application September26, 1939, Serial No. 296,596

6 Claims. (01. 265-1) Our invention relates to drilling equipment foruse in oil or gas wells or the like, and is more specifically directedto weight indicating means for determining the total weight of thesuspended drilling equipment as the string of pipe and the bit. When thebit is set on the bottom of the well the unsuspended weight is usuallyreferred to as the weight on the bottom. Our invention is not confinedto drilling equipment but may be used generally to indicate weight ofheavy apparatus.

The present application is related to our previously filed copendingapplication Serial No. 268,500, entitled Oil well strain gauge, filedApril 18, 1939, and is an improvement of the copending application of B.F. Langer which has matured into Patent 2,275,532 and S. L. Burgwin,Serial No. 258,510 entitled Strain gauges illed February 25, 1939, whichhas matured into Patent 2,231,702 and assigned to the present assignee.

When drilling a well with rotary drilling equipment, it is important toknow: (1) the weight on the bit, that is, the unsuspended weight, (2)the total weight on the drill string, (3) the suspended weight of thedrill string, and (4) the pull being exerted'when pulling on a stuckdrill stem or stuck casing. It is particularly important to know theweight on the bit because that weight affects the (a) rate ofpenetration, (b) duration of bit sharpness, (c) straightness of hole,(d) life of the drill stem, (e) life of drilling bit, and (f) wobble ofdrill stem against side of hole. It is apparent that improper weight onthe bit can easily increase the cost of drilling, as insuflicient weightmeans reduced rate of penetration, and excessive weight means extraexpense and loss of time due to shortened life of equipment, prematuredulling of bit, and possibly fishing for broken tools.

The present commonly used device for indicating these loads is a shuntdynamometer placed on the tail rope of the hoisting cable. It isactuated by the pull on the cable attempting to straighten a kink in thecable which is made when mounting the gauge on the tail rope. Theaccuracy of the device is affected by the friction of the sheaves in theblocks, and by the bending of the cables over the sheaves. Also, as thenumber of lines between blocks is changed, the proper dial must beplaced on the gauge in order that it may indicate the total suspendedload.

The weight on the bit is determined by observing the weight of thesuspended string when of! bottom, then setting the tool on bottom untilthe indicated weight has decreased by that amount desired as the load onthe bit. This reduction'iii weight is usually referred to as the weighton bottom.

Our invention covers a new arrangement of one or more magnetic straingauges which may be placed within an elastic element which is mounted inthe string of suspended equipment above the ground surface. It consistsessentially of a single, a compound, or a multiplicity of strain gaugesin conjuction with a reference rod mounted on the centerline of theelastic element. The arrangement is such that the elongation of adefinite portion of the elastic element is transmitted mechanically tothe strain gauge (or gauges). By proper electrical circuits andinstruments, the total load and the reduction in load as the tool is seton bottom are indicated and recorded. 7

The device must have a very high accuracy when measuring the weight onbottom. For example, suppose the total weight of a suspended drillstring is 200,000 pounds. It is desired to maintain weight on bottom of20,000 pounds within limits of +500 pounds. Such a variation is +25% ofthe weight on bottom, but only +25% of the total weight.

Tests have shown that such accuracy is not possible with an instrumentmounted in the tail rope.

In order to avoid (1) the inaccuracy of the measurement in the tailrope, (2) the use of a bulky elastic element in series with the hook,and (3) the need for very high precision in the voltage regulation andrecording instruments, we propose, in accordance with our invention, theuse of a compound electric strain gauge mounted in the shank of thelifting hook.

An object of our invention is to provide a compound electric straingauge which will accurately determine the total weight of the string ofdrilling tools when suspended freely from the hook, and which will alsoindicate with accuracy the weight on the bottom, that is, the totalweight on the bit when the bit is in contact with the bottom of thewell.

Another object of our invention is to provide a new type of compoundmagnetic strain gauge and to dispose it in such manner in the string ofdrilling tools so as to take up a minimum amount of space and causeminimum added length to the string and at the same time to be effectiveto indicate weights with precision.

Other objects and advantages will become more apparent from a study ofthe following specificaof the hook incorporated in Fig. 1 showing thedisposition of a compound magnetic strain gauge within the shank of thehook;

Fig. 3 is an enlarged sectional view of the compound magnetic straingauge incorporated in Fig.

2 takenalong line III-III' of Fig. 4.

Fig. 4 is a partial-side view of the strain gauge taken along line IV-IVof Fig. 3; and

Fig. 5 is a schematic showing of a pair of electrical metering circuits,each of which includes an impedance bridge which includes a pair ofcoils of a single magnetic strain gauge; and

Fig. 6 is a front view in cross-section of a modification of ourinvention.

Referring more particularly to Figure 1, the numeral denotes an oil welldrilling derrick, at the top of which is supporteda crown block 2 whichcarries a plural-wound cable 3, which cable supports-a traveling block4. The traveling block 4 supports a block bail 5 which in turn supportsa hook bail 6, the latter finally yieldingly supporting a hook I throughintermediary elements hereinafter described. Supported on hook I is aswivel and a string of pipe forming the drill string 3 of anyconventional type. One end of cable 3 is wound about a drum 9 of anyconventional type. It is thus seen that by applying power to the drum,the hook is raised, and by applying braking pressure to the drum, the

hook is held at any desired height. .An electrical cable III, whichsupplies electrical energy to the compound magnetic strain gauge mountedin shank H of the hook (which will appear more clearly in Fig. 2), isshown supported halfway up the derrick in order to allow full travel ofthe hook, finally leading to a pair of meters I2 and I3 located near theground surface.

\ Fig. 2 shows the hook in greater detail. Pivoted on the hook bail 6 isa support member H which has screw-threaded on the top thereof a sleevel5. Surrounding shank H is a helical spring l6 which supports a pair ofrace plates II which in turn support a nut l8, which nut isscrew-threadedly connected to the upper end of hook shank II. The hookshank II has drilled therein from the top or upper end thereof a cavitywhich is suitably shaped so as to accommodate a compound magnetic straingauge IS. The details of the compound magnetic strain gauge are moreclearly shown in Fig. 3, which is an enlarged sectional view thereof.

Referring more particularly to Fig. 3, the compound magnetic straingauge I 3 comprises essentially a pair of electromagnets and 2|, whichare separated by a partition member 22 made of brass or other suitablenon-magnetic material for magnetically separating the two electromagnets23 and 2|. Each of the electromagnets 20 and 2| is of the constructiondescribed in detail in our copending application previously referred to.Briefly, each of them, such as 20, comprises an armature 23 which isrigidly fastened to. an armature framework 24, which in turn is rigidlysecured to a top plate 25 and screw-threaded pin 25a. Threaded to pin25a is a cap assembly 26 which is rigidly secured to a cylindrical shell21, which in turn is rigidly secured to a flanged pipe 28 which isthreaded at 23- to the shank ll. Thus, in efiect, it will be seen thatthe two armatures (one from each electromagnet 20 and 2|), such as 23,are rigidly connected through the medium of a number of elements formedsubstantially as a box to'the point 29. The cylindrical shell 2'! has ahole surrounded by an insulating ring 21a through which cable i0 is ledto energize the electromagnets. The electromagnet 20 has cooperatingwith the armature 23 a core structure 30, upon which is wound a pair ofcoils 3| and 32. The core structures of both of the electromagnets 20and 2| are rigidly supported on partition 22 by suitable rivets asillustrated in Fig. 3 by a cross-section taken partly along line lIL-IIIof Fig. 4 and are secured to a common screwthreaded pin 33 which isintegral with a reference rod 34. The bottom of the reference rod 34 isscrew-threaded at point 35 to the shank Thus, in-efiect, the core andthe coils mounted thereon are secured by meansof a number ofintermediary elements to point 35. The hook shank H is made of asuitable elastic metal which will stretch or elongate a desirable amountas a result of the weight of the drilling string of tools supported bythe hook,

As the shank stretches as the result of increased weight on the hook,points 29 and 35 in Fig. 3 are pulled farther and farther apart. Hence,armature 23 moves somewhat farther from coil 32a, but moves closer tocoil 3 la, thereby changing the effective magnetic path and theimpedances of coils 3Ia and 32a. It should be noted that point 29 isselected so as to be located below the threads of the nut I8. This isdone because the threads carry the entire load, and- Hence theredistribution of loads due to creep would tend to introduce inaccuracyin the magnetic strain gauge if point 29 were located within theconfines of the threaded section; that is, if

point 29 were chosen immediately adjacent the electromagnetic structureof the strain gauge.

The construction of the magnetic strain gauge is such that it can beassembled into the hook shank and all the threaded connections securelytightened without damaging the more delicate parts of the gauge. Theflanged pipe 28 is first screwed into the shank with a suitable wrench.The strain gauge itself, consisting of parts 20, 2|, 22, 23, 24, 25,25a, 30, 3| and 32 is then connected to the rod 34 by means of the screwthreaded pin 33, The rod 34 is then passed through the pipe 28 andthreaded into the shank at 35. Part 22 moves longitudinally relative topart 25. After this, the cylindrical shell 21 and the cap 26 are easilyinstalled to complete the assembly.

In order to minimize temperature errors, the space surrounding thereference rod 34 and the compound electromagnet is filled withtransformer oil to keep the rod and electromagnets at the sametemperature as the hook shank. The cylindrical shell 21 is made of thesame material as the armature framework 24 and the partition 22 to whichthe electromagnets are attached. Also the rod 34 is made of the samematerial as the hook shank ll so that temperature changes will notproduce errors.

One of the main difficulties encountered when pound magnetic straingauge, as described below,

suflicient accuracy can be obtained for both weight on bottom and totalload measurements of the drilling string of tools without using extremeaccuracy in the regulation of the voltage applied to the gauge. Theschematic circuit of the proposed gauge is shown in Fig. 5. It is, ineifect, two independent magnetic strain gauges, one for measuring totalload and the other for measuring weight on bottom." The bridge circuitof the total load gauge including coils Ma and 32 and variableinductance coil 38 is adjusted so that balance is obtained atzero totalload." The current flowing through the meter at any given load is thenproportional to the load and to the applied voltage, and a voltagechange of 2% will produce an error of 2% in the load reading, which wecan assume is within the required accuracy. The bridge circuit of the"load on bottom" gauge is adjusted so that balance is obtained at zerobit pressure" instead of at zero hook load. The current flowing throughthe load on bottom" meter is thus proportional to bit pressure andvoltage, so that a voltage change of 2% produces an error of only 2% inthe pressure reading. If the same gauge were used for both total loadand load on bottom then for the weights assumed hereinbefore, a voltageshift of 2% would produce of error in the bit pressure reading, whichcould not be tolerated.

The compound gauge can be made in various ways. It can take the form oftwo independent gauges located at different points along the stringsuspended from the derrick, or it can be made as a single gauge withdouble windings. If it is not necessary to obtain simultaneous readingsof total load and bit pressure, a single gauge can be used with two setsof controls (1. e. immdance bridge metering circuits) and means forswitching a single electromagnet back and forth from one set of controlsto the other.

In some instances coils 3i and 32 may be connected in series with avariable inductance such as 31 to form a magnetic bridge circuit.However, in order to minimize the introduction of error due to bendingof the hook shank, it is preferable to connect diagonally opposite coilsof the compound strain gauge in each ofthe bridge circuits; that is, forexample, in one bridge circuit the upper left-hand coil 3| of Fig. 3 isconnected with the lower right-hand coil 32a, thus, together with thevariable inductance coil 31, forming one of the bridge circuits, whichbridge circuit is connected to a meter l3 which may be either anindicating, recording or a combined indicating and recording type ofelectrical meter suitably calibrated to read "load on bottom." if of thedirect-current milliammeter type, will also include a rectifier,preferably a bridge type copper oxide rectifier (not shown), inasmuch asthe source of supply is an alternating-current source, as shown. Meterl3 may be calibrated to indicate the load on the bottom. Adjustableresistors 49 and 50 are provided so as to make it possible to set thepointer of meter II to zero while the total load is still suspended.Likewise the meter il, in a similar bridge circuit embodying theremaining two coils 32 and 31a Meters l2 and I3,

of the compound electromagnetic structure, is

has been shown as being positioned within the hook shank, it will beapparent that it may likewise be positioned in other parts of the stringsuspended by the derrick, either above or below the hook shank. Forexample, it-may be a separate unit which is added between the hook ball8 and the block ball 5, or which separate unit may be inserted somewherealong the string 3 of the drilling tools. In some instances, it is moredesirable to mount it in parts other than the hook, because by so doinga conventional type of hook may be used rather than to make the hook ofspecial construction.

Fig.- 6 illustrates a modification of the strain gauge mounting in whichthe strain gauge unit is mounted on a structure which is independent ofthe hook and which can be attached to the lower removable ball of thetraveling block, or in fact to any element in the suspended string.Numeral l0 denotes an elastic element which has a hole 4i drilled orbored on the axis thereof and being of suitable dimension to accommodatea magnetic strain gauge unit. Numeral 41 denotes a cap nut connected onone end of the elastic element. This cap nut permits introduction of thestrain gauge unit and assembly of yokes l3 and 44 on the element. Asecond cap nut ll is also shown but this could be integral with theelastic element. Balls 46 and 41 respectively engage the bails of thetraveling block and the hock. Qne of these bails must be removable.Numeral 48 represents the removable trunnions of the yoke 44 which isnecessary so that ball 41 can be removed so that it may be connectedwith the hail of the hook. The strain gauge unit, the means for lockingthe cap nut, and the means for bringing out the leads of the gauge arenot indicated but are substantially the same as illustrated in theprevious embodiment.

The embodiment shown in Fig. 6 results in a minimum of overall length ofthe strain gauge unit since yokes 43 and 44 cover the same longitudinalspace as that taken up by elastic element 40. Other means for openingbail 41 for engagement with the bail of the hook are of course possible.For example, the lower portion of this bail may be a separate piece withclevis ends secured to the ends of the upper portions or arms of theball by removable pins. The outstanding advantage of the modificationillustrated in Fig. 6 is that the strain gauge is a unit which isseparate and independent of the hook or of any other element of thestring so that it can be used with any standard equipment in the string,so that a standard type of hook can be used. In the previously describedmodification, the hook had to be modified to accommodate the straingauge.

To summarize, we propose an instrument for indicating and recording thetotal load and the reduction in total load when the bit is set on thebottom of the well (the "weight on bottom") on a rotary well drillingrig. The instrument consists of a compound magnetic strain gauge (or acombination oi gauges) so mounted with the hook shank that the strain ina portion of the shank of the lifting hook is measured. Some of theadvantages of our specific strain gauge over other devices which havebeen used or proposed are:

(1) It avoids the errors due to frictional losses in the hoisting systemby making the measurement in the hook instead of the tail rope.

(2) It puts the measuring device in a protected location, and where itis not in the way of the operator.

(6) It avoids the necessity for extreme accuracy in voltage regulationby using two independent bridge type strain gauges, one for "total loadand the other for load on bottom.

We are, of course, aware that others particularly after having had thebenefit of the teachings of our invention, may devise other devicesembodying our invention, and we, therefore, do not wish to be limited tothe specific showings made in the drawings and the descriptivedisclosure hereinbefore made, but wish to be limited only by the scopeof the appended claims.

We claim as our invention:

1. In a drilling apparatus for wells and the like, a hook for supportinga drilling string of tools, said hook having a substantially cylindricalshank portion, said shank portion having an elongated cavity locatedinside thereof along its axis, a magnetic type strain gauge whichincludes an electromagnet and an electrical metering circuitelectrically connected thereto which provides a zero reading for a fullysuspended load, said electromagnet being mounted within said cavity andhaving its core and its armature rigidly attached to spaced concentricthreaded connections on said shank and being adapted for relative motionas the result of separation of said spaced connections due to elongationof said shank due to the load of said drilling string of tools,partition means extending substantially along the axis or said shankportion for rigidly supporting said core, said electrical meteringcircuit being adjusted to give a reading inversely proportional to theelongation of said shank portion.

2. In a drilling apparatus for wells and the like, a hook for supportinga drilling string of tools,.said hook having a substantially cylindricalshank portion, said shank portion having an elongated cavity locatedinside thereof along its axis, a magnetic type strain gauge whichincludes an electrical impedance bridge circuit, an electromagnet havinga pair of coils and armature means movable therebetween, said coilsforming two legs of said bridge circuit, metering means electricallyconnected to said bridge circuit which provides a zero reading for thestring of tools when fully suspended, said electromagnet being mountedwithin said cavity and having its core and its armature rigidly attachedto spaced threaded, concentric parts of said shank and being adapted forrelative motion as the result of separation of said spaced parts due toelongation of said shank due to the load of the drilling string oftools, said electrical metering means thereby being adapted to providean indication of the weight on bottom of said drillin string of tools.

'3. In a drilling apparatus for wells and the like, a hook forsupporting a drilling string of ed between said electromagnets andmechani-v cally supporting the two cores thereof, two impedance bridgecircuits, each of which includes one of each of said pair of coils astwo of its legs, two impedance means, each forming the other two legs ofthe respective bridge circuits, said electromagnets being mounted withinsaid cavity and having its cores and armatures rigidly attached tospaced parts of said shank and being adapted for relative motion as theresult of separation of said spaced parts due to elongation of saidshank due to the load of the drilling, a pair of electrical meters eachelectrically connected to one of said bridge circuits for measuringdifferent portions or said load depending upon whether said drillingstring of tools is supported or unsupported at the bottom thereof.

4. In a drilling apparatus for wells and the like, a hook for supportinga drilling string of tools, said hook having a substantially cylindricalshank portion, said shank portion having an elongated cavity locatedinside thereof along its axis, a magnetic type strain gauge whichincludes a pair of electromagnets each comprising a pair of coils on acore and an armature movable between said coils, a non-magneticpartition member located between said electromagnets and mechanicallysupporting the two cores thereof, said electromagnets being mountedwithin said cavity and having their cores and armatures rigidly attachedto spaced parts of said shank and being adapted for relative motion asthe result of separation of said spaced parts due to elongation of saidshank due to the load of said drilling string of tools, a pair ofmetering circuits, each connected to one of the coils of each of saidelectromagnets and each being adapted to indicate the amount of load onsaid hook for various positions of said drilling string of tools.

5. In a drilling apparatus for wells and the like, a hook for supportinga drilling string of tools, said hook having a substantially cylindricalshank portion, said shank portion having an elongated cavity locatedinside thereof along its axis, a magnetic type strain gauge whichincludes a compound electromagnet structure comprising in effect twoseparate electromagnets, each of which has a pair of coils on its corestructure a and an armature movable therebetween, a partition memberlocated between and mechanically interconnecting the cores of eachelectromagnet, two impedance bridge circuits, each of which includes oneof each of said pair of coils as two of its legs, variable inductancecoils, each forming the other two legs of the respective bridge cirsaidload depending upon whether said drilling string of tools is supportedor unsupported at the bottom thereof.

6. In a drilling apparatus for Wells and the like, a hook for supportinga drilling string of tools, said hook having a substantially cylindricalshank portion subjected to strain by the weight of said string of tools,said shank portion having an elongated cavity located inside thereofalong its axis, a nut which is screw threaded to the top of said shankportion for forming a sealed enclosure, support means for suppoi'thigsaid. nut thereby imparting strain to threaded por tion due to theweight of said string of tools, a magnetic type strain gauge whichincludes an electromagnet and an electrical metering circuitelectrically connected thereto, said electromagnet being mounted withinsaid cavity and having its core and its armature rigidly attached tospaced concentric, threaded pa s of said shanlz, both of which are belowsaid so "hr-eaded con nection and being adapted to. relative motion asthe result of separation of spaced parts due to elongation of said shankdue to the load of the drilling string of tools, said eieotrioalmetering circuit ther h vide an ind: string of tools.

ED'W 1 BERNARD 1;

